问题 问答题

如图装置实验,A、B两烧杯分别盛放200g10%NaOH和足量CuSO4溶液.通电一段时间后,c极上有Cu析出,又测得A杯中溶液的质量减少4.5g(不考虑水的蒸发).

请回答下列问题:

(1)电源P极为______极;请分别写出b极和c极上发生的电极反应式:______;______

(2)c极上析出固体铜的质量为______g

(3)若装置中用铅蓄电池作电源,已知铅蓄电池放电时发生如下反应:

负极:Pb+SO42-=PbSO4+2e-

正极:PbO2+4H++SO42-+2e-=PbSO4+2H2O

假设在a极制得气体0.050mol,这时电池内消耗的H2SO4的物质的量至少是______mol.

答案

(1)c极上有Cu析出,说明c为电解池的阴极,d为阳极,则P为负极,b为电解NaOH溶液的阳极发生反应为4OH--4e-=2H2O+O2↑,c为电解硫酸铜溶液的阴极,发生反应为Cu2++2e-=Cu,

故答案为:负;4OH--4e-=2H2O+O2↑;Cu2++2e-=Cu;

(2)A总反应式为2H2O

 电解 
.
 
2H2↑+O2↑,A杯中溶液的质量减少4.5g,应为电解的水的质量,n(H2O)=
4.5g
18g/mol
=0.25mol,转移电子为0.5mol,c极上析出固体铜的物质的量为0.25mol,质量为0.25mol×64g/mol=16g,

故答案为:16;

(3)a极制得气体0.050mol,因为氢气,转移电子0.10mol,铅蓄电池总反应式为Pb+PbO2+2H2SO4=2PbSO4+2H2O,则电池内消耗的H2SO4的物质的量至少是0.10mol,

故答案为:0.10.

单项选择题 A1/A2型题
问答题

It is hard to predict how science is going to turn out, and if it is really good science it is impossible to predict. If the things to be found are actually new, they are by definition unknown in advance. You cannot make choices in this matter. (46)You either have science or you don’t, and if you have it you are obliged to accept the surprising and disturbing pieces of information, along with the neat and promptly useful bits.

The only solid piece of scientific troth about which I feel totally confident is that we are profoundly ignorant about nature. Indeed, I regard this as the major discovery of the past hundred years of biology. It is, in its way, an illuminating piece of news. (47)It would have amazed the brightest minds of the 18th century Enlightenment to be told by any of us how little we know and how bewildering the way ahead seems. (48)It is this sudden confrontation with the depth and scope of ignorance that represents the most significant contribution of the 20th century science to the human intellect. In earlier times, we either pretended to understand how things worked or ignored the problem, or simply made up stories to fill the gaps. Now that we have begun exploring in earnest, we are getting glimpses of how huge the questions are, and how far from being answered. Because of this, we are depressed. (49)It is not so bad being ignorant if you are totally ignorant; the hard thing is knowing in some detail the reality of ignorance, the worst spots and here and there the not-so-bad sports, but not true light at the end of the tunnel nor even any tunnels that can yet be trusted.

But we are making a beginning and there ought to be some satisfaction. There are probably no questions we can think up that can’t be answered, sooner or later, including even the matter of consciousness. (50)To be sure, there may well be questions we can’t think up, ever, and therefore limits to the reach of human intellect, but that is another matter. Within our limits, we should be able to work our way through to all our answers if we keep at it long enough, and pay attention.

(49)It is not so bad being ignorant if you are totally ignorant; the hard thing is knowing in some detail the reality of ignorance, the worst spots and here and there the not-so-bad sports, but not true light at the end of the tunnel nor even any tunnels that can yet be trusted.